Lighting systems are used to illuminate display cases, such as commercial refrigeration units, as well as other display cases that need not be refrigerated. Typically, a fluorescent tube is used to illuminate products disposed in the display case. Fluorescent tubes do not have nearly as long a lifetime as a typical LED. Furthermore, for refrigerated display cases, initiating the required arc to illuminate a fluorescent tube is difficult in a refrigerated compartment.
Light emitting diodes have also been used to illuminate display cases. Known lighting systems for retail display cases that use vertically oriented point light sources, e.g. light emitting diodes (“LEDs”) disposed along a vertical axis, to illuminate products in the display case typically throw light in an angular distribution pattern along the horizontal direction. FIG. 1 depicts a customer C of typical height, e.g. between about 5 feet to about 6 and ½ feet, standing on a viewing surface, which can be the floor F adjacent a display case 10. LEDs 12 (depicted schematically—the LEDs would not be visible from outside of the case) direct light in a generally horizontal direction to illuminate retail products 16 supported on shelves 18 (only one product and one shelf shown for clarity) in the display case.
As LEDs have become more powerful and able to generate more light, it has been found to be desirable to reduce the number of LEDs used to illuminate a retail display case. Since LEDs typically have higher luminance (intensity per unit area) than fluorescent sources, and since LEDs are typically used in conjunction with optics to emit into a narrow beam pattern, this can result in challenges to overcome.
Light that impinges on products 16 having a glossy finish specularly reflects off of the glossy surface. Specular reflection is where the angle of incidence of the light ray with respect to a normal surface of the product 16 is equal to the angle of reflection. If a customer's C eyes are in the path of the specularly reflected light rays, then the customer sees a glare on the product surface. This obscures the customer's view of the products in the display case, which is undesirable.